The invention relates generally to the field of equipment that incorporates multiple mandrels for temporarily receiving work pieces upon which a process must be performed, where it is sometimes necessary to quickly retract or reposition a mandrel. More particularly, the invention relates to such equipment wherein the mandrel needs to be retracted in a direction perpendicular to the longitudinal axis of the mandrel.
A mandrel is typically a cylindrical member used to retain another object during a processing operation. For example, in equipment used in the printing of beverage cans, a large number of freely rotating mandrels are mounted about the perimeter of a large rotating drum. A blank can is placed onto each mandrel at a loading station, and the drum then rotates the loaded mandrel past an applicator or printing mechanism, such as a rotating wheel having a series of inked printing blankets. The can loaded onto the mandrel contacts the printing blanket and ink is transferred in a precise manner. After inking, a varnish or lacquer is often applied as a sealant in the same manner. This type of equipment is designed to handle large quantities of cans in a very short time. For example, a typical decorating machine of the type described having from 24 to 36 equally spaced mandrels may produce over 2000 printings per minute.
In the event a can is not properly loaded onto a mandrel, ink or varnish will transfer onto the mandrel itself due to the thinness of the can wall and the minimal tolerances present in the equipment. If this occurs, ink or varnish will be transferred to the interior of the next blank can loaded onto the mandrel unless the equipment is shut down and cleaned. Where production totals of hundreds of thousands of cans per day are required, a shut down for even a few minutes is costly.
Because of this, when a blank can is not properly loaded onto a mandrel, the decorating machine is designed to detect this condition by known sensing means and to trigger a trip or can skip event. The trip event typically consists of the rotating applicator drum or the can handling component being shifted slightly away from the printing blanket component so that ink is not transferred onto an empty mandrel. In current equipment, a trip event may result in incomplete printing of 3 or more cans preceding and following the empty mandrel, such that these cans will be rejected by quality control. In addition, the current mechanism for enacting the trip event requires movement of large sections of the equipment, which entails complicated mechanisms that are susceptible to failure and wear. Examples of trip structures and systems designed to address the problem of unloaded or misloaded mandrels are shown in U.S. Pat. No. 3,665,853 to Hartmeister et al., U.S. Pat. No. 4,441,418 to Hahn, and U.S. Pat. No. 4,491,613 to Hahn, which show equipment wherein the applicator or printing means is retracted in response to occurrence of a trip event, and U.S. Pat. No. 3,563,170 to Cvacho et al., U.S. Pat. No. 3,851,579 to Zurick, U.S. Pat. No. 4,018,151 to Urban et al., U.S. Pat. No. 4,037,530 to Sirvet, and U.S. Pat. No. 4,140,053 to Skrypek et al., which show equipment wherein the mandrel support means is retracted in response to the trip event. These patents provide an overview of the general problem and descriptions of representative equipment found in the industry, and therefore the disclosure of these references is incorporated herein by reference.
A mandrel trip apparatus was disclosed in my U.S. Pat. No. 6,840,166, which addressed several problems inherent in the prior art at the time. The disclosure of this reference is incorporated herein by reference. This patent provides an independent mandrel trip apparatus having an operational mechanism of improved efficiency and durability, wherein a trip event only affects the non-loaded mandrel, in that each mandrel mounting block is provided with means to retract its mandrel without effect to the adjacent mandrels. In this patent, the mandrel support block retaining the mandrel is connected to a mounting block in a manner such that the mandrel support block can be reciprocatingly retracted and extended relative to the mounting block in a direction perpendicular to the longitudinal axis of the mandrel. A cam follower is connected to the mounting block, the mounting block being connected to the drum or plate by a pair of guide shafts positioned within guide bores disposed in the drum or plate, whereby the mounting block is able to reciprocate in the radial direction in response to movement of the cam follower.
In use the mandrel and the mandrel trip apparatus are subjected to high stress. Because the mandrels and mandrel trip apparatus are mounted to the plate member only on one end, the stresses are disproportionally distributed, such that the free end of the mandrel is susceptible to displacement from its optimum position. The disproportionate stresses can result in misalignment, the need for more frequent adjustment and repair, and eventual failure.
It is an object of this invention to provide a novel and improved assembly for such a mandrel trip apparatus, wherein the mechanism for connecting the mounting blocks to the drum or plate comprises linear bearing rail guides and linear guide rails. It is a further object to provide such an assembly wherein the mounting blocks are retained between a pair of plate members such that support is provided at both the front and rear.